diff --git a/etc/inc/gwlb.inc b/etc/inc/gwlb.inc
index cfbfcc595..c2c61d066 100644
--- a/etc/inc/gwlb.inc
+++ b/etc/inc/gwlb.inc
@@ -966,7 +966,7 @@ function get_interface_gateway($interface, &$dynamic = false) {
 	}
 
 	// for dynamic interfaces we handle them through the $interface_router file.
-	if (!is_ipaddrv4($gw) && !is_ipaddrv4($gwcfg['ipaddr'])) {
+	if (($gw == NULL || !is_ipaddrv4($gw)) && !is_ipaddrv4($gwcfg['ipaddr'])) {
 		$realif = get_real_interface($interface);
 		if (file_exists("{$g['tmp_path']}/{$realif}_router")) {
 				$gw = trim(file_get_contents("{$g['tmp_path']}/{$realif}_router"), " \n");
@@ -996,7 +996,7 @@ function get_interface_gateway_v6($interface, &$dynamic = false) {
 	}
 
 	// for dynamic interfaces we handle them through the $interface_router file.
-	if (!is_ipaddrv6($gw) && !is_ipaddrv6($gwcfg['ipaddrv6'])) {
+	if (($gw == NULL || !is_ipaddrv6($gw)) && !is_ipaddrv6($gwcfg['ipaddrv6'])) {
 			$realif = get_real_interface($interface);
 			if (file_exists("{$g['tmp_path']}/{$realif}_routerv6")) {
 				$gw = trim(file_get_contents("{$g['tmp_path']}/{$realif}_routerv6"), " \n");